The present invention relates generally to nickel-hydrogen batteries, and more particularly, to nickel-hydrogen batteries having wettable porous gas diffusion screens inserted during the fabrication process.
Nickel-hydrogen batteries typically comprise a multiplicity of individual cells stacked "back-to-back" during manufacture. In at least one commercially available design, each of these cells comprises a plurality of nickel oxide and teflon-platinum hydrogen electrode elements in a sufficient number to form a cell stack. Each of the cell stacks is separated from those adjacent on either side by a porous gas diffusion screen. In use, the cell stacks are filled with an alkaline electrolyte by a commonly used vacuum procedure. In batteries produced today, inherently hydrophobic polypropylene gas diffusion screens are typically employed and, in use, it is found that these hydrophobic gas diffusion screens tend to trap electrolyte within them. Further, when the batteries must be drained during manufacture, it is found that these gas screens also tend to retain some amount of the electrolyte because there is simply no wettable path out of the screens, even when pressurized hydrogen gas is forced through their interior. This retained electrolyte contributes to the uneven distribution of oxygen gas during overcharge, especially when the batteries are cycled horizontally on earth or in spinner-type spacecraft. This uneven oxygen distribution has led to a problem known as "edge popping" which comprises an explosive reaction of hydrogen and oxygen within a cell. This can result in a destruction of the edge of the stack and partial shorting of the battery cell. In addition, this retained electrolyte leads to blockage and uneven distribution of hydrogen gas pressure within the battery, thus further contributing to degraded performance of the battery.